These odd-looking shoots are not diseased but are the result of a fairly common condition known as "fasciation" that affects shoots on all sorts of plants quite randomly and for no apparent reason, but presumed by plant experts to be the result of damage to buds just as the shoots were starting to form. There is therefore nothing to be alarmed about and you should simply cut off the shoots that are unsightly. […] Fasciation can also affect, with somewhat more visually catastrophic results, various spire-forming herbaceous plants such as delphiniums and hollyhocks.